Embodiments of the disclosure relate generally to wind turbines and, more particularly, for mitigating loads during yaw error conditions experienced by wind turbines.
A utility-scale wind turbine typically includes a set of two or three large rotor blades mounted to a hub. The rotor blades and the hub together are referred to as a rotor. The rotor blades aerodynamically interact with the wind and create lift and drag, which is then translated into a driving torque by the rotor. The rotor is attached to and drives a main shaft, which in turn is operatively connected via a drive train to a generator or a set of generators that produce electric power. The main shaft, the drive train and the generator(s) are all situated within a nacelle, which rests on a yaw system that continuously pivots along a vertical axis to keep the rotor blades facing in the direction of the prevailing wind current to generate maximum torque.
In certain circumstances, the wind direction can shift faster than the response of the yaw system, which can result in a yaw error. Yaw error is typically defined as the difference (e.g., angular difference) between the orientation of the wind turbine nacelle and the wind direction and occurs when the wind turbine nacelle is not aligned with the wind. During such aforementioned transient wind events, the yaw error, which can be sustained for a few seconds or minutes (until the yaw system points the wind turbine nacelle to face the wind), might damage the wind turbine if operation of the wind turbine continues. Specifically, during such operation of the wind turbine, yaw error can result in unacceptably high loads on the rotor blades, hub, tower, and other components thereof, which can result in damage.
Yaw error can be avoided by actively adjusting the orientation of the wind turbine nacelle with the yaw system, i.e. by keeping the wind turbine nacelle pointed directly into the wind. However, as mentioned above, the wind direction may shift quite rapidly and faster than the response of the yaw system. A technique proposed in the past handles extreme yaw error by simply shutting down the wind turbine in those extreme yaw error conditions and then restarting once the wind turbine nacelle is properly oriented into the wind. When the wind turbine shut down is initiated, it goes through a shut down cycle and then a startup cycle, which results in several minutes of lost energy production. In addition, high mechanical loading can occur on turbine components if the shutdown procedure is not tailored to an extreme yaw error condition.
Therefore, there is a need for new and improved control systems and methods for mitigating loads during extreme yaw error on a wind turbine.